Smith, of Birkenhead, Wirral, tried to claim Teddy suffocated after slipping under the water in the bath.

The child-killer can be heard sobbing as he calls emergency services – describing Teddy as “blue”.

As the call handler tells him how to perform CPR, Smith yells “come on, just come on” at the tot.

Sentencing Smith, Mr Justice Garnham said Teddy's death was caused by a internal tear to the wall of his abdomen.

LIVERPOOL ECHO

MUM: Ashleigh Willett has already admitted cruelty to her children

“You struck him in the gut with such force to cause that internal bleeding”

Mr Justice Garnham

He said: "I cannot say whether you punched him or kicked him or used your knee on him but I'm quite certain that you struck him in the gut with such force to cause that internal bleeding."

He added: "I cannot speculate what might have caused that loss of temper but something, probably something trivial, happened in that house that lunchtime that caused you to fly into a rage and strike Teddy Tilston."

Teddy was found unresponsive by paramedics at the couple's home on March 1 after Smith rang emergency services to say he found the boy unconscious in the bath.

As well as the internal tear, he had a bleed on the brain likely to have been caused a week before his death, and bruises to his head, ear, upper lip, neck, jaw, abdomen and back.

LIVERPOOL ECHO

HEARTBROKEN: Teddy with his natural father Marc Tilston

Mr Justice Garnham said: "I've no doubt that your frustrations and short temper had resulted over the previous few weeks in numerous other injuries to Teddy and Cassidy.

"Not all but the majority of bruises on the bodies of the twins were caused, I'm sure, by your actions.

"It's plain that you have a vicious temper and, without compunction, you took that temper out on the young children in your care."

The trial heard Willett was not at home when Teddy died because she had taken Cassidy to hospital.

She returned home from work as a barber earlier in the day after Smith, who was looking after the children, told her Cassidy had knocked herself unconscious after running into a table.

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When nurses at the hospital examined Cassidy they also found she had a fractured wrist which she may have suffered up to six months earlier as well as a catalogue of bruises.

Icah Peart QC, defending, said Smith was an inexperienced "de facto step-parent" to the children and their older sister Darcie, three.

He said Smith's remorse had been apparent "from the word go".

A victim personal statement by the twins' dad, Marc Tilston, was given to the judge but was not read out in court.